Multivibrator



Aug. 4, 1953 (L M IL IL WITN ESSES:

WHEELER 2,648,004

MULTIVIBRATOR Filed May 12, 1948 4 Cathode Vol'fdzye I I a armrm Volfaye a! 6140' 15 W 0 kfenfihl INVENTOR v Myron Wheeler.

ATTORNEY Patented Aug. 4, 1953 2.6 8.004 MULTIVIBRATOR Myron S. Wheeler, Upper Montclair, N. J., as-

signor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 12, 1948, Serial No. 26,562

2 Claims.

My invention relates to oscillation generators and, more particularly to oscillators of the multivibrator type.

Apparatus illustrative of the prior art of which I am aware is shown in the White Patent 2,185,363. By extensive experiment with thecircuit shown in Figure 1 of the White patent I have found that this circuit will only produce at its output terminals saw tooth wave shapes. It is desirable in many applications to have a multivibrator that will produce any one of a number of wave forms. One example of this necessity is in test racks where it is desirable to obtain different wave forms from the same terminals. In radar equipment a square wave form impulse of short duration and of either positive or negative polarity serves to key the transmitter or to trigger one of the several components requiring synchronization. An oscillation generator for delivering such an impulse is desirable. An oscillation generator for delivering a variety of wave shapes for blocking purposes in radar and television systems is also desirable.

It is accordingly an object of my invention to provide an oscillation generator which shall deliver at its output a plurality of wave forms.

A more specific object of my invention is to provide a multivibrator capable of delivering oscillations of widely different wave forms at its output.

Another object of my invention is to provide a single multivibrator which shall be applicable for a multiplicity of uses.

A further object of my invention is to provide a multivibrator capable of rapid rates of change of voltage.

A still further object of my invention is to provide a multivibrator which shall be eflici'ent in operation.

An ancillary object of my invention is to provide a multivibrator which shall have a low output impedance.

In accordance with my invention I provide a resistance coupled, cathode loaded, multivibrator having at least two discharge devices. The, devices are so connected that there is zero phase shift across each. A signal impressed or produced at the input returns after traversing both discharge devices to the input in such a phase as to reinforce the voltage that is already present. The oscillation of the multivibrator is determined by the time constant of the coupling circuit and the discharge device characteristics. By varying the magnitudes of the capacities and resistances of the multivibrator circuitany one tential through a resistance !25.

2 of a plurality of wave forms can be produced at its output terminals.

The novel features that I consider character: istic of my invention are set forth with particularity in the appended claims. The invention it-,- self, however, both as to its organization and'its method of operation together with additional objects and advantages thereof will be understood from the following description of specific embodiments when read in connection with the accompanying drawing in which:

Figure 'l is a diagram of a circuit embodying my invention. Y

Figures 2A, B, C, and D are graphs illustrating the operation of the circuit shown in Figure 1,

Figure 3 is a graph showing several of the wave forms that can be produced at the output terminals of the apparatus shown in Figure 1.

The apparatus shown in Figure 1 comprises a pair of discharge devices 3 and 5 which are shown as of the triode type but may be of the pentode or other type. These discharge devices 3 and 5 may also be contained in a single envelope. Each of these discharge devices 3 and 5 has an anode I and 9 respectively, a cathode H and I3 respectively, and a control electrode I 5 and I1 respectively. Both discharge devices 3 and 5 have a common resistance l9 connected to their cathodes II and [3, the other side of the resistance I9 being connected to the negative side of a direct current source of potential. This potential may be derived from a commercial supply through a rectifier or from a battery or from other facilities.

The first discharge device 3 has a connection from its control electrode l5 through a coupling capacitor 2| to the anode 9 of the second discharge device 5. There is also a connection from the control electrode 15 of the first discharge device 3 through a resistance 23 to the cathodes H p and I3 of the discharge devices 3 and 5. The

anode 1 of the first discharge device 3 is connected directlyto the positive side of the direct current source of potential. The anode 9 of the second discharge device 5 is connected to the positive side of the direct current source of po- The control electrode 11 of the second discharge device 5 is connected to the junction of a capacitor 21 and a resistance .29 which are in series, the resistance end of this series network being connected to the cathodes H and I3 of the discharge devices 3 and 5. The capacitor end of this series unit is connected to the negative side of the direct current source of potential.

The operation of the circuit will now be described with reference to Figures 1, 2A, 2B, 2C, and 2D. In Figures 2A to 2D, voltage is plotted vertically and time horizontally. Points along any vertical line extending through the graphs represent the same instant of time. As labeled curve A is a plot of the cathode voltage as a function of time, curve B, of the voltage at control electrode 15, curve C of the voltage at control electrode l1, and curve D of the voltage at anode 9.

The voltage of the cathodes of, the discharge devices 3 and 5 when the first discharge device 3 is conducting is representd'by the straight line from a to b in curve A. The value of the voltage on the control electrode [5 of the first discharge device 3 while it is conductin 'is'represented in curve B by the sloping line between a andb. The rising loop a-b of curve C represents the voltage 'cntnecontrol electrode I1 of the second discharge device 5. The straight line ab of curve 'D represents the voltage appearing at the anode 9 ofthe'scc'onddischarge device I will assume for purposes of describing the operation of the equipment that initially the first discharge device 3 is conducting and the second discharge device 5 is non-conducting. As the device 3 conducts, current flows through resistor I9. By reason of the drop in potential across this resistor, capacitor 21 is charged with its upper plate positive and its lower plate negative. The voltage on the control electrode l1 of the second discharge device 5 which is connected to the upper plate of capacitor 21 therefore rises as represented in curve (1 (loop a-b). When this potential has reached the value represented by the instant I) in curve C the second discharge deviee i'starts to conduct and the voltage of its ant-a6 '9 is decreased decreasing the voltage on the control electrode H5 or the first discharge device 3 'th' ough the coupling capacitor 2|. The volt'age 'on the control electrode continues to decreas between instants b and c as represented by the loop bc "n curve B.

r The current now through the first discharge de'vice3 decreases'as the voltage on control elec- "t'rc'jde"l5fdecreases and begins to decrease at the instant 'b (Figure 2). The decrease of current llo'wthjoiigh'the'first discharge device 3 is at a higher rate than'is'the increase of flow of current in the second'discharge device Sbecause of the gain of the'first discharge device 3. As the current flow through discharge device '3 decreases, t'he'c'iirrent'flow through the common resistor l9 "decreases. This decrease results in a decrease in'the voltage on the cathodes II and I3 of the discharge devices Sand 5. The voltage or these cathodes now falls as represented by the loop between D ankle in curve A. Because the'current flow through resistorlil decreases, the voltage on capacitor 21 and the control electrode l1 decreases. Thistlecrease is represented by the loop 'b-cof curve C and the corresponding decrease of the anode .voltage of discharge device 5 by loop b--c of curve D.

During the interval 11-0 the voltage on the cathodes H and I3 and the voltage on the control electrode [1 are both decreasing. The conductivity ofdischarge V .the voltage between control electrode [1 and cath- "ode I3; it does not necessarily decrease as the grid voltage decreases and may as a matter of fact increase. In the same interval the conductivity of the discharge device 3 alsodependentv on the relative relationship of the cathode podevice 5 is determined by,

the circuit constant.

tential and the potential of control electrode I5 (that is the potential of anode 9) and does not necessarily follow the potential of control electrode l5 alone.

The potential of control electrode l1 and cathode |3 will eventually reach a magnitude at which the conductivity of discharge device 5 begins to decrease. The conductivity of discharge device 3 will as a result increase and this increase will result in a further and amplified decrease in the conductivity of discharge device 5 and increase in conductivity of discharge device 3. Discharge device 5 will therefore quickly become non-conductive and discharge device 3 conductive. This condition occurs at instant c and is represented by the vertical lines in curves A, B, C and D at instant c. The second discharge device 5 is now out off since its cathode voltage has now returned to its original magnitude, that is to the magnitude at which the first discharge device is fully conductive.

The above described operation continues to repeat itself producing at the output terminals 30 ahd 3| the desired wave form. The duration of the transition which occurs between instants b and band its character is dependent primarily on the magnitudes of the resistors 19 and 29 and the capacitor 21. Any one of a plurality of wave forms canbe'obtained by varying the magnitude of the common resistor I9, the capacitor 21, and the resistance 29 holding the other elements of 7 However, to obtain a still further number of wave forms all of the capacitors and resistances shown in Figure 1 can be made variable.

Figure 3 shows several of the wave forms that can be obtained by varying the common resistance 19, the capacitor 21, and the resistance 29.

, To produce the wave shape shown in Figure 3a the resistance l9 should have a magnitude oi the-orderof 10,000 ohms, the resistance 29 0.5 megohm, and the capacitor '21 0.05 micro- -fara d. This wave shape consists of negative pulses having slightly curved tops alternating with positive pulses of saw tooth wave form of thesame duration. By amplification and clipping this wave form can be converted into a series of negative fiat top pulses spaced at intervals equal in duration to the pulses. By control adjustrnent of the magnitudes of the resistors and capacitor the negative pulses can be further flattened.

-To produce/the wave shape shown in Figure 3b in 'which the negative pulses are the same as in Figure 3a but the positive pulses are of longer duration than the negative pulses, the

resistance [9 should have a magnitude of the order of 25,000 ohmsythe resistance 29 0.5 megohm, and the capacitor 21 0.05 microfarad.

The wave shape'sli'own in Figure 3c in which the negative pulses are'the same as in Figure 3a but the positive pulses are of shorter duration than the negative pulses, is produced by using a magnitude of'the order of 25,000 ohms for the resistance l9, 0.1 meg'ohin for the -resistance 29 and 0 05 m icrofarad'for the "capacitor '21.

To produce the wave shape shown in Figure 3d ;the resistance is should have a magnitude or the 'or der'of 2 5,00'0'oh'r'ns, the resistance 29 0.1 megohr'n, and-thebapa cit'or 21' 0.005niicrofarad.

Thiswave "shape consists of negative pulses havlin g'fsubstantiall fiat tops alternating with posit ve pulses of s'a'wtooth'wave lorm of much shorter duration than "the negative pulses.

' 'To' tide-ace the wave shape shown in FigureBe the resistance [9 should have a magnitude of the order of 25,000 ohms, the resistance 29 5 megohms, and the capacitor 21 0.005 microfarad. This wave shape consists of negative pulses having substantially fiat tops alternating with positive pulses of saw tooth wave form of much longer duration than the negative pulses. These positive pulses are of longer duration than the positive pulses shown in Figure 3b, however, the negative pulses have approximately the same duration as the negative pulses shown in Figure 3b.

Of course it is to be understood by those skilled in the art that these examples of wave forms are only a few of the wave shapes that can be produced. Other wave shapes can be obtained by choosing different values for the resistances l9 and 29, and the capacitor 21 as well as changing the values of the other capacitor and resistances in the circuit shown in Figure 1.

Although I have described the wave shapes shown in Figures 3a to 30 as having alternate negative and positive pulses these wave shapes can, by the proper positioning of the voltage reference line consist of all negative or all positive pulses. By amplification and clipping these wave forms can be converted into a series of all negative or all positive flat top pulses.

The circuit shown in Figure 1 has a low output impedance although it is not constant since the apparatus is now linear. The output impedance is approximately equal to the reciprocal of the grid-plate transconductance of the conducting discharge device at any given instant in the cycle of operation.

Tubes suitable for use as discharge device 3 are a 6J5, a 6AC5 and a 6C5 and the tubes suitable ior discharge device 5 are a 6AK5, a 6SJ7, a GAG? and a 681-17. However it is to be understood that other tubes may serve equally as well as the invention is not limited to the use of only the above mentioned tubes.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as m invention:

1. In combination, a first and second terminal for connection to a source of potential, first and second discharge devices, each including at least an anode, a cathode, and a control electrode, means connecting the anode of said first discharge device to said first terminal, means connecting the anode of said second discharge 6 device through a resistor to said first terminal, a first capacitor connected between the control electrode of said first discharge device and the anode of said second discharge device, a resistance connected between said control electrode of said first discharge device and its cathode, a pair of output terminals, a resistor capacitor network consisting of a parallel circuit, one leg of which is a resistor, of the order of between 10,000 ohms and 25,000 ohms, the other leg of which is a resistor, of the order of between 0.1 megohm and 5 megohms, connected in series with a capacitor, of the order of between 0.05 microfarad and 0.005 microfarad, the resistor terminal of said network being common to the cathodes of said discharge devices and one of said output terminals, the capacitor terminal of said network being common to said second terminal, and the other said output terminal, a connection from the terminal of said network capacitor remote from said second terminal to the said control electrode of said second discharge device.

2. In combination, a first and second discharge devices, each having an anode, a cathode, and a control electrode, means for applying anode potentials to said discharge devices, a first capacitor connected between the control electrode of said first discharge device and the anode of said second discharge device, a resistance connected between said control electrode of said first discharge device and its cathode, a pair of output terminals, means rendering one of said output terminals and said cathodes common, a resistor capacitor network comprising a second capacitor connected between said control elec-q trode of said second discharge device and the other of said output terminals, a resistor connected between the control electrode and cathode of said second discharge device, and a resistor shunting said output terminals, at least one of the elements of said resistor capacitor network being variable, whereby a plurality of different wave forms may be produced at said output terminals.

MYRON S. WHEELER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,185,363 White Jan. 2, 1940 2,440,992 Webb May 4, 1948 OTHER REFERENCES Radar Electronic Fundamentals Navships 900,016, Bureau of Ships, Navy Department. Copy available in the Scientific Library (pages 202 to 206). 

